Regarding double-flange differential pressure level gauges

This post was last edited by ylb913 on 2017-4-30 09:07. I recently participated in the replacement of a level gauge. Due to the need for negative migration – where the negative pressure is higher than that of the positive pressure side, and this pressure difference corresponds to the height of the liquid column made up of isolants such as ethylene glycol or silicone oil; this height actually represents the measurement range – along with the density of the medium being measured, the actual measurement signal within the 0%–100% range is always negative pressure. So it’s the same: whether there is positive or negative pressure inside the device, for a double-flange gauge the zero point and the 100% range are determined by the pressure of the liquid column, that is, the negative drift plus the pressure of the liquid column of the medium being measured; this has nothing to do with the operating pressure of the device.

I’ve never tried such an application; let’s make a guess. If there is vacuum on the low-pressure side, then that side will have positive pressure, and the high-pressure side also has positive pressure. The pressure difference = high – low

I can understand what you mean, but what about this calculation process? I tend to get bogged down in details; I want to see the calculation process in order to identify the factors that affect the accuracy of the liquid level. (PS: The level gauges I use sometimes show incorrect levels, which affects the yield, so I want to determine the reasons through the calculation process and eliminate or reduce these effects.)

:How can the low-voltage side be at positive pressure?

Take the actual calculation process that just took place as an example: since it is necessary to replace the gauge used for measuring the liquid level, the calculations are done in the instrument workshop, the range is adjusted, and then the gauge is installed on-site and put into use – this process has nothing to do with the operating pressure of the equipment. The basic formula is P=ρgh, with the unit being pa; dividing by 1000 gives kPa. The range height is 1.29 meters. We are using diol, with a specific gravity of 1.11. The measurement is taken at the interface between water (ethanolamine solution) and liquefied gas; the density of water is taken as 1007 kg/m3, while the density of liquefied gas is 520 kg/m3. 1. The negative migration value is = -1.11*9.81*1.29 = -14.05 kPa. 2. When the interface percentage is 0%, the mixture consists entirely of liquefied gas; the measured pressure is = -14.05 + 0.52*9.81*1.29 = -14.05 + 0.58 = -7.47 kPa. 3. When the interface percentage is 100%, the mixture consists entirely of ethanolamine aqueous solution; the measured pressure is = -14.05 + 1.007*9.81*1.29 = -14.05 + 12.74 = -1.30 kPa. Look, the actual measurement values throughout the process are all negative pressure, and there’s no need to consider the operating pressure of the equipment.

I’m guessing; I’m wrong. Pressuring the low-pressure side creates positive pressure, while evacuating creates vacuum, so it should be negative pressure. Differential pressure = high pressure – (-low pressure). It’s just a guess – I’ve never done this before

This post was last edited by ylb913 on 2017-5-1 06:04. Differential pressure = pressure on the positive side – pressure on the negative side. Double flange, with silicone oil as the isolation fluid; it is assumed that a 30% alkaline solution is being measured (the specific gravity of 30% alkaline solution is 1.32), and the range height is 1.4 meters. When the liquid level is at 0%, the operating pressure is not taken into consideration; the pressure on the positive-pressure side is 0, while the pressure on the negative-pressure side is equal to ρgh resulting from the height difference of the isolation fluid. Assuming the specific gravity of silicone oil is 0.93, the pressure difference measured at 0% is = 0 – 0.93*9.81*1.4 = -12.77 kPa. At 100% liquid level, the pressure difference = (1.32–0.93) * 9.81 * 1.4 = +5.36 kPa

Are these two diaphragms the same? Do we mean low pressure and high pressure only in terms of the manufacturing process? Are there no differences between high and low pressure for these two diaphragms?